Orthogonal Frequency Division Multiplexing Access (OFDMA)
Orthogonal Frequency Division Multiplexing Access (OFDMA) is used in 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) and the Worldwide Interoperability for Microwave Access (WiMAX) networks. The available spectrum is partitioned into orthogonal subcarriers. The orthogonality among the subcarriers can reduce intra-cell interference (ICI). In LTE networks, base stations are connected via a mesh of so-called X2-interfaces.
Inter-Cell Interference (ICI)
In the context of OFDMA, inter-cell interference (ICI) occurs when adjacent cells assign the same frequency to different user equipment (UE) or MSs. The most severe ICI originates from the frequency collision on the edges of the cells. If the frequency in which the BS1 communicates with MS1 on the edge in one cell is the same as the frequency in which the BS2 communicates with MS2 on the edge of an adjacent cell, then the interference has the greatest impact in both downlink and uplink directions.
Physical Resource Block (PRB) or Radio Resource Block (RRB)
The controllable radio resource in OFDMA network has three aspects: frequency, time and space. The resource element considered in the invention is the physical resource block (PRB), which spans both the frequency and time domain. The PRB is also known as the Radio Resource Block (RRB). The component frequencies of one PRB can be either contiguous or disjoint. The time duration of the PRB is defined by Transmission Time Interval (TTI). By reusing the PRB among cells or sectors of cells, frequency division, time division and spatial division are achievable.
Inter-Cell Interference Coordination (ICIC)
Inter-Cell Interference Coordination (ICIC) can effectively reduce ICI in cell-edge regions. ICIC aims to allocate disjoint channel resources to a cell-edge MS and a potentially interfering MS(s) in an adjacent cell. By careful coordination between the cell-edge MS and its interfering MS(s), the ICI can be greatly reduced.
Cell-Edge and Cell-Center
To avoid frequency collision, various frequency reuse schemes are known in the prior art. The most straightforward method assigns non-overlapping bandwidth (BW) to adjacent cells. This enables the elimination of frequency collision at the cost of spectrum efficiency. To overcome this drawback, soft and fractional frequency reuse, (FFR) have been described. Both schemes partition the BW into two parts: cell-edge BW and cell-center BW.
Within each cell, User Equipment (UE) or mobile stations can be partitioned into two groups. Cell-edge UEs are assigned to cell-edge BW, while cell-center UEs can use the cell-edge bandwidth, when available. Usually the cell-edge BW takes a ⅓ fixed portion of the entire BW. The transmit power on each BW can be changed adaptively according to the interference level.
Primary and Secondary UEs
The UEs can be partitioned into two groups based on a priority of the UEs. UEs with highest priority to the radio resource are primary UEs, such as police, ambulance, etc. Secondary UEs have to terminate their transmission when the occupying resources are required by a primary UE.
Base Station Cooperation (BSC)
Base station cooperation (BSC) enables multiple BSs to transmit signals to a single MS concurrently while sharing the same resource, i.e., time and frequency, using beam forming.